1. Field of the Invention
The invention relates to a fuel injection control apparatus.
2. Description of the Related Art
Internal combustion engines (engines) are equipped with catalysts for controlling exhaust gas. For example, in the case where such a catalyst is overheated by high temperature exhaust gas or the like, the exhaust gas control capability of the catalyst sometimes declines. The decline in the exhaust gas control capability of a catalyst occurs due to the catalyst temperature rising above the activation temperature of the catalyst, or the like. In order to maintain good level of the exhaust gas control capability of the catalyst, a technology of increasing the amount of fuel injection so that due to the increased vaporization heat of injected fuel the temperature of exhaust gas declines and therefore the catalyst is cooled is sometimes used. The increase of fuel in this technology is termed OT (over-temperature protection) increase. The amount of increase of fuel achieved by the OT increase is termed OT increase value.
Japanese Patent Application Publication No. 7-166918 (JP-A-7-166918) discloses a technology that prevents overheating of a catalyst by calculating the OT increase value. Japanese Patent Application Publication No. 2003-343242 (JP-A-2003-343242) discloses a technology that estimates the temperature of a catalyst according to the rotation speed and the load of an internal combustion engine, and that performs an OT determination regarding the catalyst (a determination as to whether or not the catalyst is overheated) on the basis of the estimated temperature of the catalyst.
However, as for the foregoing related-art technologies, it sometimes happens that, the fuel injection amount is excessively increased by the OT increase, resulting in increased amounts of exhaust emissions, for example, carbon monoxide (CO), hydrocarbons (HCs), etc., or deteriorated fuel economy.